1. Field of the Invention
This invention is concerned with vortex tubes. More particularly, the present invention relates to design and construction of vortex tubes.
2. Description of the Prior Art
An early development in connection with vortex tubes is discussed in U.S. Pat. No. 1,952,281 to Ranque, which discloses a method for obtaining from a compressible fluid under pressure, a current of hot fluid and a current of cold fluid, whereby the initial fluid is transformed into two separate currents of different temperatures free of any mechanical assistance.
All of these results take place in an instrument having no moving parts and which is extremely compact in size and in some cases no larger than a pencil.
There is no universally accepted theoretical explanation of the energy separation phenomenon or the vortex effect. Nevertheless, there are many designers who have been working in the field of vortex design, who design vortex tubes based on previous experience and experimentation.
A conventional counterflow vortex tube comprises a tube with a diaphragm closing one end of the tube and a small hole in the center of the diaphragm, one or more tangential nozzles piercing the tube just inside the diaphragm, and a throttle valve at the far end of the slender tube.
A function of the counterflow vortex tube is to receive a flow of compressed gas through nozzles and to discharge a stream of cold, expanded gas through a small hole in the diaphragm, and a stream of hot, expanded gas through the valve.
The intensity of the energy exchange in the vortex tube is conventionally measured by the value of the enthalpy or the temperature differences of the "cold" .DELTA.T.sub.1 stream and of the "hot" .DELTA.T.sub.2 stream. EQU .DELTA.T.sub.1 =To-T.sub.1 EQU .DELTA.T.sub.2 =T.sub.2 -To (1)
where:
To=temperature of the gas ahead of the vortex tube inlet nozzles; PA1 T.sub.1 =temperature of the "cold" gas downstream from cold diaphragm; and PA1 T.sub.2 =temperature of the "hot" gas downstream from valve. PA1 Cp--gas specific heat; PA1 s--relative area of the vortex tube's nozzles which is defined as total area of all of the nozzles (F) divided by the area of the vortex tube in the nozzle cross section ##EQU4## where Do is the vortex tube diameter; d--relative diameter of the diaphragm which is defined as diaphragm diameter divided by vortex tube diameter Do; PA1 .mu.--cold fraction; PA1 P--relative pressure ratio which is defined as the gas pressure ahead of the vortex tube nozzles divided by gas pressure downstream of the diaphragm. PA1 P=pressure ratio=gas pressure ahead of the vortex tube nozzles divided to gas pressure downstream the diaphragm PA1 .mu.=cold fraction=mass flow of cold gas divided by mass flow of the inlet gas PA1 s=relative area of the nozzles ##EQU5## d=relative diameter of diaphragm=d.sub.1 /Do and wherein when P is 5.0 or less and more than 1.0 and d is between approximately 0.4 and approximately 0.55 and .mu. is between 0.4 and approximately 0.65, then s is selected to be between 0.08 and approximately 0.12; and
Further developments heretofore were concerned with the design and construction of vortex tubes as disclosed in U.S. Pat. No. 3,208,229 to Fulton, which is primarily concerned with the design and construction of vortex tubes capable of emitting colder and hotter streams of gas.
The problems indicated by Fulton still exist, and it is still desirable to develop and design vortex tubes capable of operating with sufficient efficiency and economy which would make it possible to revolutionize portions of such technological fields as refrigeration, air conditioning, cryogenics, instrumentation, and controls.
The efficiency or excellence of the vortex tube in performing its function is measured by how little gas pressure it requires and how much temperature difference it produces for a given cold fraction. (Cold fraction=mass flow of cold gas divided by mass flow of inlet gas.) A thermodynamic formulation of the problem of optimizing the design of the counterflow vortex tube is that given the kind of gas, its pressure, temperature, and rate of flow, and a certain cold fraction to be delivered at a certain lower pressure, there exists a combination of geometric dimensions of all the parts of the vortex tube such that the cold gas will be delivered at the lowest possible temperature.
According to Fulton, the optimization problem may be solved only by performing a very large number of parametric experiments where one dimension and another are changed step by step and the gas temperatures measured.
Fulton taught that at least fifteen important dimensions exist which can be taken into consideration in the design for a vortex tube. This poses a problem of such intricacy that to achieve a thorough optimization even for one operating condition, it is very tedious and expensive. Should any condition be changed, a new optimization is required. For this reason, it is believed that research is likely to continue on vortex tubes indefinitely.
I have also worked on vortex tube design, prior to my invention, and developed a vortex tube using the then conventional experimental methods and designed a vortex tube having the features, as disclosed in the Soviet publication/monograph published by the Gas Industry, pertaining to Natural Gas, Gas Condensate, Field and Plant Treatment. The publication title is: "Vortex Tube Application In The Layout Natural Gas Field Treatment", Number 5 of 1979.
A development was based on a parametrical definition of the cold temperature differences which was offered in the above-noted Soviet publication. ##EQU2##
A hot temperature difference is easily calculated from energy balance: ##EQU3## where: W--velocity of the gas in the vortex tube nozzles;
That is, according to (2), the vortex effect is a function of the some few vortex tube variable operational and design parameters.
The total length of the vortex tube Lo, that is, a distance between a tangential nozzle cross section and a throttling valve at the far end of the tube is not a vortex tube variable parameter. It was disclosed in the Soviet publication/monograph that efficiency of the vortex tube may be obtained using the "long" that is Lo/Do approximately 20, vortex tube. The vortex tube having Lo/Do ratio less approximately than 20 is inefficient. Increase of the Lo/Do ratio over approximately 20 is irrelevant (has no effect) to the temperature differences value.
In the experimental study which was set, due to complexity of the theoretical solution relations of (2), some "step by step" changes of the parameters were performed. It was found that, while changing the value of the "s" parameter for any fixed pressure ratio P (P .ltoreq.4) and, having .mu. and d parameters unchangeable (.mu.=0.5; d=0.5), then an efficient vortex tube was obtained with value of the relative area of the nozzles equal 0.1 (s=0.1).